判断一个IP地址是否合法，并判断该地址是否属于一个给定子网。从而考察读者是否对IP地址概念及其子网划分有非常清楚的认识。-To determine the legality of an IP address and determine whether the address belongs to a network to the stator. In order to study whether the reader the concept of IP addresses and subnetting has a very clear understanding.